Various implantable medical devices have been developed that receive information from one or more physiologic sensors or transducers. A typical physiologic sensor transduces a measurable parameter of the human body, such as blood pressure, temperature or oxygen saturation for example, into corresponding electrical signals. At the appropriate time, the physiologic data acquired by an implantable medical device is uplinked to an external receiving system, such as a programmer, for storage and analysis.
In many implantable medical device applications, a radio frequency (RF) telemetry technique is used by which data acquired by an implantable medical device is impressed on a carrier signal and transmitted to an external receiving system during a data uplink procedure. A demodulator is typically provided in the receiving system that recovers the physiologic information signal from a modulated signal received from the implantable medical device. In many receiving systems, differences between Q's (i.e., shape factor or quality factor) of the transmitting and receiving antennae result in corruption of the transferred signal in a non-controlled way, such as introduction of undesirable bit-to-bit amplitude variations.
Most conventional receiving systems employ an analog design or, alternatively, a mixed analog/digital design for the receiving system circuitry. As such, most conventional receiving systems are typically implemented using a "custom" design approach, which is both expensive and limited in terms of the potential to use standardized, readily available, and relatively inexpensive electronic components. Using analog components in a particular design is generally associated with increased power consumption, in contrast to a fully digital implementation. Increasing the power consumption requirements of the receiving system may pose a problem in portable and small scale applications.
A traditional receiving system implementation which utilizes an analog or mixed analog/digital design may also be relatively intolerant to frequency variations in the data transmitted by the implantable medical device. A more precise, and therefore more expensive, telemetry methodology employed in the implantable medical device is often required to address such frequency variation intolerance in conventional designs.
Various implementations of RF telemetry systems designed for use with an implantable medical device are known in the art, examples of which may be found in the issued U.S. Patents listed in Table 1 below.
TABLE 1 Patent No. Inventor(s) Issue Date 4,281,664 Duggan August 4, 1981 4,494,545 Slocum et al. January 22, 1985 4,556,063 Thompson et al. December 3, 1985 4,562,840 Batina et al. January 7, 1986 4,571,589 Slocum et al. February 18, 1986 4,681,111 Silvian July 21, 1987 4,757,816 Ryan et al. July 19, 1988 4,949,299 Silvian July 31, 1990 5,058,581 Silvian October 22, 1991 5,107,833 Barsness April 28, 1992 5,127,404 Wyborny et al. July 7, 1992 5,241,961 Henry September 7, 1993 5,264,843 Silvian November 23, 1993 5,292,343 Blanchette et al. March 8, 1994 5,300,093 Koestner et al. April 5, 1994 5,312,453 Shelton et al. May 17, 1994 5,383,912 Cox et al. January 24, 1995 5,475,307 Silvian December 12, 1995 5,620,472 Rahbar April 15, 1997
The patents listed in Table 1 hereinabove are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of Various Embodiments, and the claims set forth below, many of the devices and methods disclosed in the patents identified below and listed in Table 1 above may be modified advantageously by using the teachings of the present invention.